A variety of known systems exist with the purpose of reducing flammability in aircraft fuel tanks. Such systems may be known by a number of designations including, but not limited to, On-Board Inert Gas Generation System (OBIGGS), Nitrogen Generation System (NGS), Flammability Reduction System (FRS), Fuel Tank Inerting System (FTIS), etc. However, a commonality among the systems involves reducing the oxygen content of fuel tank ullage by feeding inert gas into the fuel tank. Often, the systems produce nitrogen-enriched air (NEA) for the inert gas. Air with lower percent oxygen is less flammable.
Inerting systems used to produce nitrogen-enriched air may rely on pressure swing absorption and desorption from media as a separation mechanism or diffusion through polymer membranes as another separation mechanism to remove oxygen. In systems with polymer hollow fiber membranes, compressed air enters the bore of the polymer hollow fiber and oxygen permeates through the polymer hollow fiber walls. The oxygen permeate is collected and exhausted overboard. The remaining nitrogen-enriched retentate flows through the bore and is collected at the air separation module product gas outlet for distribution to aircraft fuel tanks. Unfortunately, service life of the air separation module and the system operating conditions may be limited by the polymers used in construction of the gas separation module. Accordingly, increased reliability of air separation modules is desirable.